1. Technical Field
The present invention relates to a probe card, and more particularly, to a probe card for testing high-frequency signals.
2. Background
Generally, it is necessary to test the electrical characteristics of integrated circuit devices at the wafer level to verify the performance of the integrated circuit device and to confirm the device satisfies the product specification. Integrated circuit devices with electrical characteristics satisfying the specification are selected for the subsequent packaging process, and the other devices are discarded to avoid incurring additional packaging cost. Another electrical property test is performed on the integrated circuit device after the packaging process is completed to screen out the below-standard devices to increase the product yield. In other words, the integrated circuit devices must undergo several electrical tests during the manufacturing process.
During testing, the probes of the probe card are moved to contact different devices or different pads of the same device, transmit test signals, and receive measured signals. As the integrated circuit device technology develops toward higher frequency and greater density, the probes must be designed with correspondingly greater density. In addition, the probe card must be equipped with proper shielding against EMI (electromagnetic interference) to prevent the probes from being interfered with by EMI.
FIG. 1 illustrates a conventional probe card 1 for testing high-frequency signals. The probe card 1 includes a high-frequency probe 11 fixed on a circuit board 12, a coaxial cable 13 electrically connecting one distal end 111 of the probe 11 to a signal terminal 121 of the circuit board 12, and a shield layer of the coaxial cable 13 electrically connected to a ground terminal 122 of the circuit board 12. To achieve effective shielding, the exposed portion of the distal end 111 of the probe 11 must be as short as possible, and the electrical connection between the probe 11 and the signal terminal 121 should be implemented by the coaxial cable 13 with high shielding ability.
The central conductor of the coaxial cable 13 is covered by a thick insulator to provide the desired impendence, and the thick insulator results in a large size of the coaxial cable 13. Consequently, although the probes 11 can be densely positioned for high-frequency testing, the large size of the coaxial cable 13 does not allow similarly dense positioning, and this kind of probe card 1 cannot be applied to high-frequency testing.
FIG. 2 illustrates another conventional probe card 2 for testing high-frequency signals. The probe card 2 includes a circuit board 22 and a coaxial probe 21 fixed on the circuit board 22, and the distal end of the coaxial probe 22 is connected to a signal terminal of the circuit board 22. The coaxial probe 22 includes a metal shielding layer 223 covering an insulating layer 221. Similar to the coaxial cable 13 shown in FIG. 1, the thick insulating layer of the coaxial probe 21 results in a large size, which cannot be positioned in a high density manner, and this kind of probe card 2 cannot be applied to high-frequency testing.
In addition, the conventional electrical connection, which uses the wires of the coaxial cables between the distal end of the probe and the circuit board, causes the distal ends of the probes to terminate at different positions, which increases the difficulty of connecting the probes to the circuit board. In particular, for the probes arranged with high density, the wires connected to the distal ends of the probes may push each other, causing a disorderly arrangement, which may influence the quality of the signal transmission.